code for vertical drop for toilet/tub, IPC

So long story short, need to create some space for a new more efficient HVAC duct setup in my crawl space. The new duct run goes under my guest bathroom which includes a sink, toilet and tub all along the same wall. The plumbing runs right through the center of the space and I want to tuck it up between the floor joists for a few feet over before dropping down and tieing into the end of the main line.

Is there a minimum drop for the tub and toilet before you should elbow it over? Toilet is 3" and rest is 2" dropped down to 1.5" right before connecting to the tub/sink vertical run.

There would be no limit to vertical drop AFTER a trap, so the toilet is no problem. There ARE codes about the vertical drop of a tailpiece BEFORE the trap. I don't have the numbers on top of my head...someone will get it for us.

It is NOT always possible to just "raise" the drain lines, and still maintain all the requirements for them, such as proper venting. HOW you raise the lines may be more important than whether you can do it.

I'm not completely positive that its "properly" vented now. As it stands, tub and toilet are not directly vented. I believe the sink is though its in the wall where I cannot directly verify. There is however a vent on the roof 2 stories up, so I believe it is vented.

I'll post pics later when I can get to my scanner to show you what I'm talking about, but sink and tub are wye'd into the main 4" together with the run from the tub to the wye being 3-5' with a proper p-trap under the tub drain. I about 1.5' up from where the sink/sub wye in, the main drain is elbowed up 90 degrees directly into the toilet flange. This all takes place about 1' under the bottom of the floor joists (approx 22" from subfloor - 10" floor joists).

What I want to do is cut back everything about 4' to more or less directly under the sink/vent. Then take the main 4" up into a double wye that reduces to 3" for the toilet and 2" for the sink and tub. The double wye will have its top opening slightly under the bottom of the floor joists and be angled about 45 degrees from the floor joists. The angle allows for the tub and toilet connections which are directly side by side in the cavity between the floor joists to run next to each other without getting in the way. Within the 10" deep floor joists, I'd elbow the toilet over to the center wye opening. The tub's p-trap would be moved up so that the bottom of it was within the 10" deep space between the floor joists and rotated just a bit such that the run over to the wye is offset to the side of the 3" toilet train. Then the sink is just connected up with a couple 45s and off we go. I'll probably also want to leave cleanouts under the toilet/shower so those elbows will probalby be wyes in the end that are capped off.

I think the tub ends up being a bit far away from the vent (3-5' - i'll measure when I have a chance), but short of ripping up the entire bathroom (which we'll do later when we remodel it), it at least eliminates some of the spaces where sewer gases could be trapped since everything comes together into a single location thats directly under the vent. Of course, the vent path for the toilet/tub will be 1-2' under the water line for the sink before it reaches "dry" vent.

If you change it, you will be required to bring it up to the current code for your location. This includes the required vents.

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Yes, thats part of what I'm trying to find out... this will be a 2 stage process though. First set the bottom cause I have to replace my A/C cause it crapped out and ducting it inadequate by today's standards and the insulation on it has deteriorated and beginning to develop mold.

Second, remodel the bathroom and fix the venting. Its just over 2' from the big wye to the toilet, so I can easily pop out the top of the big wye (replace 90 with another wye) and join back into the existing vent with the sink above the water line to get the toilet vented.

The tub is just under 5' from the big wye, so working on a solution there. I'm trying to remember, but I thought you can only run like 2-3' over without venting separately. So I'm guessing I'll have to cut in with another wye there and run it up behind the wall and over into the existing vent above the sink water line. Any other creative solutions you can think of?

Yeah... all the tee looking things are actually wye + 45. Just couldnt get that detail with my crappy mushed up sharpie.

Anyone have the min code for vertical drop before a p trap?

And how would you vent the shower properly since its 5' over from the current vent ?

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You probably won't find a code minimum drop for a fixture outlet pipe. You'll find a max but not a min.

You are allowed to connect to a vent upto 6' away on an 1.5" drain when running the trap arm @ 2% grade (which is the code min usually). This rule also applies when tying into a wet vent.

What you have "proposed" in your above post is unacceptable because you appear to be s-traping fixtures. You need to tie into your vents with a fall that does not exceed the size of the pipe. This is to say that if you are running a 1.5" drain at 1/4" per foot you can run 6' before you tie into a vent because 6' at 1/4" per foot is 1.5" of total fall on the piping. So with 2" you can go 8' before you tie into a drain, etc.

So basically the tub, toilet and shower all need to tie in at the same elevation if you plan on using a 3x2" double wye to connect the fixtures.

You would be better off simply reconfiguring the plumbing so that the tub doesn't do a 180* turn to make it into the drain. If this is possible anyway. If you basically flipped the tee around that picks up the tub on the sinks wet vent you would meet minimum code requirements.

You probably won't find a code minimum drop for a fixture outlet pipe. You'll find a max but not a min.

You are allowed to connect to a vent upto 6' away on an 1.5" drain when running the trap arm @ 2% grade (which is the code min usually). This rule also applies when tying into a wet vent.

What you have "proposed" in your above post is unacceptable because you appear to be s-traping fixtures. You need to tie into your vents with a fall that does not exceed the size of the pipe. This is to say that if you are running a 1.5" drain at 1/4" per foot you can run 6' before you tie into a vent because 6' at 1/4" per foot is 1.5" of total fall on the piping. So with 2" you can go 8' before you tie into a drain, etc.

So basically the tub, toilet and shower all need to tie in at the same elevation if you plan on using a 3x2" double wye to connect the fixtures.

You would be better off simply reconfiguring the plumbing so that the tub doesn't do a 180* turn to make it into the drain. If this is possible anyway. If you basically flipped the tee around that picks up the tub on the sinks wet vent you would meet minimum code requirements.

Like this:

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Thanks for the code quote... for some reason I had 3' stuck in my head for a 1.5" drain.

Bad drawing again there I guess on my double wye. The double wye was intended to have everything enter at the same level. I see the tub looking higher than the toilet one now that you pointed it out. They are intended to run side by side. There probably needs to be a short section of straight PVC on top of the center wye to level it off with the 45 used in the shower and sink runs.

Assuming I do that, would that make the proposed alright code wise? The reason I was starting this in the first place was to get the stack tidyed up and moved over about 4' to make room for new A/C ducts. So leaving the toilet as is and fixing the 180 degree bend wont satisfy everything I need out of this.

If its better, I can elbow everything over 4' up in between the floor joists and bring it down 4' to the left and do what you have with the cleaner/straighter santee and the toilet comming in below that.

You technically shouldn't use a double wye for unvented fixtures because by doing so you'll create an s-trap. The sink is ofcourse always vented but the tub would be s-trapped. You would be better off using a double san-t not a double wye. This will also make it easier to bring out the drains on the same level.

Becareful though because your tub's drain line is only allowed to have 135* of culmlitive change between the trap and double T where it is wet vented.

So got the duct work out of the way and found a little kink in things. The vent I thought was going out the top of the sink is not. Theres actually a 4th pipe I didnt see before that goes up to catch a double vanity on the second floor bathroom before venting out the roof. This 4th pipe hooks into the 3" main line a couple feed back from where the toilet does. Thats the closest thing to venting the toilet/sink/tub in the downstairs bathroom has.

So I do still need to move everything up and out of the middle of the space, so I'm proposing the following. This gets the vent in the top rather than the bottom of everything, but is a bit on the funky side so wanted to run it by you guys.